The present invention relates to a method and apparatus for riveting metal members together for assembling automotive vehicle structures.
It is known that the manufacture of automotive vehicles often requires that metal members be attached to each other to form automotive vehicle structures. Pierce riveting is one potential method of attaching such members, particularly, metal sheets. Pierce riveting typically requires a sharpened end portion of a rivet to pierce through a first of two stacked metal sheets, and through at least a portion of a second of the stacked sheets. During such piercing, the sharpened end portion of the rivet is typically deformed or bent to secure the rivet to the sheets. For conventional pierce riveting processes, however, large amounts of force may be required to pierce through the sheets. Moreover, for higher strength sheets, the rivets may deform prior to proper piercing of the sheets or the sheets may be undesirably cracked during the riveting process. Thus, there is a need for improved pierce riveting techniques, apparatuses or both, for achieving high integrity attachment of metal members, particularly, sheets formed of refractory or high strength to weight metals such as those based on aluminum, magnesium, iron, high strength steel or the like.
The present invention meets these needs by providing an improved method of riveting a first metal member to a second metal member, with particular utility in the formation of components for an automotive vehicle. The method involves providing a piercing rivet having a central axis, a generally disk-shaped head portion and an annular portion extending outwardly from a bottom surface of the head portion, the annular portion including a sharpened piercing edge. For riveting, a first metal member is stacked on a second metal member, wherein each of the members has a first side and a second side, and at least a portion of the second side of the first member is in overlapping contact with at least a portion of the first side of the second member for forming an overlapped region. The first and second metal members are placed between a rivet assembly and a die assembly, the rivet assembly including a punch surrounded by a first electrode for contacting the first member, the die assembly including a die surrounded by a second electrode for contacting the second member, the die having a cylindrical cavity with a protrusion extending into the cavity, the first and second electrodes each connected to an electrical energy source. Thereafter, an electrical current is induced with the electrical energy source, the current flowing between the first and second electrodes and through the first and second metal members for heating the overlapped region of the first member and the second member to a more ductile condition. The rivet is driven through the first metal member and partially through the second metal member in the overlapped region such that the annular portion of the rivet is deformed radially away from the central axis to interferingly secure the rivet to the members thereby attaching the members to each other.
The present invention also provides an apparatus for riveting a first metal sheet to a second metal sheet. The apparatus includes a rivet assembly for driving a rivet through the first metal sheet and partially through the second metal sheets while the first sheet is stacked upon the second sheet. The rivet assembly includes a cylindrical punch moveable between at least a first position and a second position for driving the rivet through the first sheet and partially through the second sheet. The rivet assembly also includes a generally cylindrical binder clamp that is cylindrical about a centrally located axis, the binder clamp having a cylindrical hole that is coaxial with the axis and extends down the center of the binder clamp for receiving the punch. A cylindrical first electrode surrounds at least a portion of the binder clamp, the first electrode for contacting and supplying electricity to the metal sheets to heat the sheets prior to driving the rivet into the sheets. An insulator is disposed between the first electrode and the binder clamp for electrically separating the first electrode from the binder clamp. The apparatus also includes a die assembly for at least partially supporting the first and second sheets as the rivet assembly drives the rivet into the sheets, the die assembly. The dies assembly includes a central cylindrical die having a central cylindrical cavity defined by a circular bottom surface and an annular surface, the circular bottom surface defining a centrally located protrusion extending into the cavity. The die assembly also includes a cup shaped second electrode for conducting electricity with the first electrode, the second electrode having a generally cylindrical cavity for receiving the die. A cup shaped insulator electrically separates the second electrode from the die, the insulator receiving the die in a cavity within the insulator, the insulator being receivable within the cavity of the electrode. The apparatus also include an energy source for inducing an electrical current across the electrodes.
The present invention thus provides an improved riveting apparatus and riveting technique for providing securing piercing rivets in stacked sheets thereby more securely fastening the sheets together. The ability to locally control the temperature of the members being joined makes this invention particularly advantageous for the joining of high strength to weight metals or materials with ordinarily low ductility.